The present invention relates to a power cutoff device, and more particularly to a power cutoff device capable of suitably adjusting transient characteristics of a power voltage caused at a cutoff of the power voltage being supplied to a load circuit.
The present application claims priority from Japanese Application No. 2001-072152, the disclosure of which is incorporated herein for all purpose.
It has been known that some types of integrated circuit devices, such as an LSI and a VLSI, hybrid circuit devices of an analog circuit and a digital circuit, multi-functional, high-performance electric circuit boards having thereon mounted many electronic circuits demand more than one power voltage in order to operate in a satisfactory manner.
Such integrated circuit devices, hybrid circuit devices, and electric circuit boards (hereinafter, referred to collectively as the electronic circuit device) are generally arranged in such a manner that, as shown in FIG. 6, power input terminals P1, P2, and P3, and a ground terminal PGND provided to an electronic circuit device DVC are connected to a multi-power circuit VREG with a common ground GND, whereby a plurality of constant voltages V1, V2, and V3 generated at the multi-power circuit VREG are applied as power voltages Vcc1, Vcc2, and Vcc3, respectively.
FIG. 6 is a view showing a case where the electronic circuit device DVC is provided with three electronic circuits (hereinafter, referred to as the load circuits) LOAD1, LOAD2, and LOAD3 respectively operating on three power voltages each having a different value, and constant voltages V1, V2, and V3 generated at the multi-power circuit VREG are applied to the load circuits LOAD1, LOAD2, and LOAD3 through open/close switches SW1, SW2, and SW3, respectively.
Herein, by setting a control signal Son/off, which is outputted from an ON/OFF control circuit CNT for controlling power-up and power cutoff, to the logical level xe2x80x9cHxe2x80x9d, the open/close switches SW1, SW2, and SW3 are simultaneously closed (switched ON), whereupon the constant voltages V1, V2, and V3 are applied to the load circuits LOAD1, LOAD2, and LOAD3, respectively. On the other hand, by shifting the control signal Son/off to the logical level xe2x80x9cLxe2x80x9d from xe2x80x9cHxe2x80x9d, the closed open/close switches SW1, SW2, and SW3 are simultaneously opened (switched OFF), whereupon the constant voltages V1, V2, and V3 respectively being applied to the LOAD1, LOAD2, and LOAD3 are cut off.
According to the typical arrangement of connecting the multi-power circuit VREG to the electronic circuit device DVC as shown in FIG. 6, however, in a case where the control signal Son/off is shifted to the logical level xe2x80x9cLxe2x80x9d from xe2x80x9cHxe2x80x9d, and the constant voltages V1, V2, and V3 respectively being applied to the load circuits LOAD1, LOAD2, and LOAD3 are cut off by opening the open/close switches SW1, SW2, and SW3 at this point of change (hereinafter, referred to as the cutoff point) toff, as shown in FIG. 7 by way of example, the power voltages Vcc1, Vcc2, and Vcc3 start to attenuate to the ground level as residual voltages in their respective load circuits LOAD1, LOAD2, and LOAD3 while exhibiting different transient characteristics.
In other words, time constants related to the power voltages Vcc1, Vcc2, and Vcc3 may vary from each other depending on a difference in the standards among the load circuits LOAD1, LOAD2, and LOAD3, a difference in wiring capacitances and resistance values between the multi-power circuit VREG and each of the load circuits LOAD1, LOAD2, and LOAD3. Thus, even when the power is cut off simultaneously at the cutoff point toff, the power voltages Vcc1, Vcc2, and Vcc3 actually have different transient characteristics in the transient period after the cutoff point toff, and therefore, a time necessary to reach the ground level, an attenuation factor, etc. may vary for each.
Accordingly, voltages determined in advance by the ratings or the like which are not supposed to be applied, are applied to the load circuits LOAD1, LOAD2, and LOAD3 during the transient period since the cutoff point toff until the power voltages Vcc1, Vcc2, and Vcc3 attenuate to the ground level, which poses a problem that the load circuits LOAD1, LOAD2, and LOAD3 cause a malfunction, break, or shorten their service lives.
For example, suppose that the electronic circuit DVC may possibly cause a malfunction at the load circuits LOAD1, LOAD2, and LOAD3 unless the power voltages Vcc1, Vcc2, and Vcc3 respectively applied to the load circuits LOAD1, LOAD2, and LOAD3 are set to satisfy an inequality, Vcc1 greater than Vcc2 greater than Vcc3 during a normal operation, and during the transient period after the cutoff point toff, the power voltage Vcc3 attenuates to the ground level first followed by the power voltage Vcc1, and the power voltage Vcc2 attenuates gradually in comparison with the power voltage Vcc1. Then, as shown in FIG. 7, there is a problem that the power voltages Vcc1, Vcc2, and Vcc3 do not attenuate in accordance with the predetermined order and with predetermined voltage values because of influences of the time constants or the like.
The present invention has been devised to solve the conventional problems, and therefore, has an object to provide a power cutoff device capable of suitably adjusting the transient characteristics of a power voltage caused at a cutoff of the power voltage being supplied to a load circuit or the like, for example, a power cutoff device for allowing suitable use of various kinds of electronic circuit devices operating on more than one power voltage.
In order to achieve the above and other objects, a power cutoff device of the present invention is a power cutoff device for cutting off a power voltage being supplied to a load circuit, including: power voltage detecting means and current sink means provided between a power line and a ground line, the power line supplying a voltage generated by power means to the load circuit as the power voltage, wherein the power voltage detecting means detects a change in the power voltage generated on the power line and outputs a detection signal; and the current sink means sets a sink current corresponding to a level of the detection signal and sinks a current from the power line toward the ground line.
According to the power cutoff device arranged as above, a supply of the power voltage from the power means to the load circuit is cut off, whereupon the power voltage enters the transient state. Then, the power voltage detecting means detects a power voltage in the transient state and outputs a detection signal. The current sink means sets a sink current corresponding to the level of the detection signal, and sinks a current from the power line toward the ground line according to the sink current.
By sinking the current according to the sink current, it is possible to suitably adjust the attenuation factor of the power voltage in the transient state, a time necessary to reach the level of the ground line, etc.
Also, a power cutoff device of the present invention is a power cutoff device for cutting off a plurality of power voltages being supplied to a plurality of load circuits, including: power voltage detecting means and current sink means provided between a plurality of power lines and a ground line, the plurality of power lines supplying a plurality of voltages generated by power means to the plurality of load circuits as the plurality of power voltages, wherein the power voltage detecting means detects a change in a power voltage generated on any of the plurality of power lines and outputs a detection signal, and the current sink means sets a sink current corresponding to a level of the detection signal and sinks a current from each of the plurality of power lines toward the ground line independently.
Further, a power cutoff device of the present invention is a power cutoff device for cutting off a plurality of power voltages being supplied to a plurality of load circuits, including: power voltage detecting means and current sink means provided between a plurality of power lines and a ground line, the plurality of power lines supplying a plurality of voltages generated by power means to the plurality of load circuits as the plurality of power voltages, wherein the power voltage detecting means detects a change in a power voltage generated on each of the plurality of power lines and outputs a detection signal corresponding to each power voltage, and the current sink means sets a sink current corresponding to a level of the detection signal corresponding to each power voltage and sinks a current from each of the plurality of power lines toward the ground line independently.
According to the power cutoff devices arranged as above, when a supply of each power voltage to an electronic circuit device provided with a plurality of load circuits each operating independently on their respective power voltages is cut off, the power voltage detecting means detects at least one of power voltages in the transient state and outputs a detection signal. The current sink means sets a sink current corresponding to the level of the detection signal, and sinks a current from each power line toward the ground line independently. Hence, it is possible to suitably adjust the attenuation factor of each power voltage being applied to their respective load circuits, a time necessary to reach the level of the ground line for each, etc. Consequently, in case that the transient characteristics of the power voltages with respect to each other are determined in advance by the ratings or the like to prevent the occurrence of a malfunction of the load circuits or the like, it is possible to adequately set transient characteristics by sinking a current from each power line to the ground line independently.
In addition, the power voltage detecting means and the current sink means operate upon supply of electricity from the power voltage generated on the power line.
According to the above arrangement, a special power or the like for operating the power cutoff device can be omitted, thereby making it possible to reduce the power consumption, and downsize and simplify the circuit.
Furthermore, the current sink means sets a sink current equivalent to a value of the detection signal outputted from the power voltage detecting means and amplified by an adjustable amplification factor.
According to the above arrangement, by adjusting the amplification factor, it is possible to adequately adjust a value of a sink current. Consequently, it is possible to accurately adjust a change in the power voltage in the transient state.